摘要:

Kruskal‐Shafranov modes on a cylindrical plasma are examined with respect to possible active feedback stabilization. Active stabilization of these modes, which would make tokamak reactors more realizable, is found to be possible in principle but to present great practical difficulties. The application of the technique to a reactor‐type plasma will be considered.

ISSN:0094-243X    

DOI:10.1063/1.2948520

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

In the basic tokamak experiment, the copper shell is a highly‐satisfactory feedback control device. For certain extensions of the tokamak operation — for example, to compression heating — it is, however, convenient to remove the copper shell. External feedback control of the equilibrium position is then a natural substitute. A more complex problem is the feedback stabilization of MHD modes. The interchange instabilities, against which linear magnetic feedback is ineffective, are fortunately stabilized by the minimum‐average‐B property of the toroidal tokamak. Feedback stabilization of a type of thermal instability that results in major‐radius shifts is the principal topic of this paper.

ISSN:0094-243X    

DOI:10.1063/1.2948522

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

A sharp‐boundaried high‐&bgr; Stellarator of ℓ‐fold helical symmetry is MHD unstable, particularly to them = 1, long‐wavelength mode. For this mode the instability is driven byℓ ± 1fields introduced by the unstable displacement. Compensating fields (or, equivalently, plasma distortions) to counteract the instability can be introduced externally and controlled by a feedback arrangement. The self‐adjointness property of the MHD energy‐principle operator is used to derive the relationship between the external fields and the unstable displacement.

ISSN:0094-243X    

DOI:10.1063/1.2948523

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

An efficient method of interaction with ion modes in fusion and space plasmas through the excitation of resonant electron modes is proposed. The feasibility has been demonstrated in laboratory experiments over a wide density range (108–1010/cm3) and a wide ion frequency range (1 kHz – 500 kHz). The collisionless nature of the nonlinear interaction between electron and ion modes is emphasized leading to the feasibility of feedback stabilization in hot collisionless fusion plasmas. Measurements of nonlinear coupling coefficients are presented which support the theoretical mode‐mode coupling model.

ISSN:0094-243X    

DOI:10.1063/1.2948524

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

A modulated microwave source is used in remote feedback stabilization of the collisional drift instability in a Q‐machine cesium plasma atn ≃ 5 × 1010 cm−3. The microwave heats electrons by resonance absorption at interior plasma locations selected by adjusting the microwave frequency to the local upper‐hybrid frequency[fce2 &plus fpe2]1/2 ≃ GHz. Penetration of the evanescent exterior plasma region is achieved, by introducing a weak magnetic field gradient (∇B/ B ≈ 0.03 cm−1 « ∇n/ n ≈ 1 cm−1) with an iron block placed outside the plasma column. The modulation phase (< 180°) and microwave amplitude (≃ 0.1 mW) necessary for stabilization agree qualitatively with a linear theory including a modulated heat source. Upon stabilization, improved plasma confinement is measured.

ISSN:0094-243X    

DOI:10.1063/1.2948525

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Experimental results are reported on the feedback stabilization of a “drift‐type” instability and on the remote sensing and feedback stabilization by amplitude modulation with electron‐cyclotron resonance heating of ion‐sound instability. For the “drift‐type” instability, results are interpreted in terms of an equation of Van der Pol type; for the ion‐sound instability in terms of a theory predicting the variation of instability amplitude and frequency due to the feedback modulation of electron temperature. Comparison between the theory and experiment show good agreement.

ISSN:0094-243X    

DOI:10.1063/1.2948478

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Simultaneous suppression of several modes of the drift‐centrifugal wave in a collisionless plasma has been achieved by using as many independent feedback systems, each one tuned to a different mode. This is an improvement over broadband systems in which suppression of one mode has generally led to enhancement of other modes.

ISSN:0094-243X    

DOI:10.1063/1.2948479

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Feedback has been applied, as a diagnostic technique, to measure properties of low‐frequency instabilities. Feedback‐stabilized plasmas provide equilibria in which the temporal growth of instabilities to non‐linear saturation levels and the effect of instability on confinement can be measured by switching feedback off. Enhancement of instability amplitudes by positive feedback above the decay‐instability threshold value, can be employed to destabilize parametrically excited decay modes. Experiments with theories illustrating such feedback applications to the collisional drift instability are described.

ISSN:0094-243X    

DOI:10.1063/1.2948480

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Experimental results on the feedback control of an “edgetype” oscillation in a Q‐machine, using a fixed‐amplitude drive signal phase‐ and frequency‐locked to the plasma oscillation, are reported. Results are compared with stationary solutions of a theoretical model described by a second order linear differential equation. In connection with this theory, growth rates and a‐c coupling between suppressor probe and plasma are measured and compared with calculated values. The method provides a means of measuring radial plasma losses caused by this instability.

ISSN:0094-243X    

DOI:10.1063/1.2948481

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

A single‐ended Q‐machine has been modified to provide for the study of generalized boundary conditions. The sections of the segmented boundary can be interconnected through passive components to provide passive feedback. The ion density fluctuation amplitude of the Kelvin‐Helmholtz instability, for densities of ∼108– 109cm−3and magnetic fields of ∼1–2 kG, decreased by 20–40% when feedback is applied. The DC peak density is increased by ∼10–30% upon stabilization. The effect shows a definite dependence on the capacitance and resistance in the passive circuitry.

ISSN:0094-243X    

DOI:10.1063/1.2948483

出版商:AIP    

年代:1970

数据来源: AIP